Intimate contact with a body surface, skin for example, is especially desirable in electrotransport systems. Along with establishing an interface for ionic and/or water soluble species to diffuse, having intimate contact also insures uniform electrical current distribution, thereby avoiding high localized current densities which could cause damage to the body tissue to which the system is applied.
Important criteria for adhesive compositions utilized as in-line contact adhesives for transdermal drug delivery systems in general, are: sufficient tack for prolonged adhesion to a body surface, aggressiveness, cohesion, bio- and chemical-compatibility, rapid drug transport ability, mechanical flexibility and insolubility in water. When drugs are administered by electrotransport means rather than by passive diffusion, the adhesive must also have low resistance to ionic and water soluble drug transport and should not significantly contribute competing ionic species.
Adhesives for use with electrodes are well known in the art. Typical materials include: solvent activated adhesives such as a vinyl acrylic copolymer which is water insoluble and thus activated by acetone or a low molecular weight alcohol, U.S. Pat. No. 4,008,721, and polymerized 2-acrylamido-2-methylpropanesulfonic acid which is soluble in and thus activated by water, U.S. Pat. No. 4,391,278; and, adhesives such as karaya gum having an electrically conductive material such as an ionizable salt or a finely powdered metal dispersed therethrough, U.S. Pat. No. 4,274,420; all of which are incorporated herein by reference. While these adhesives are suitable for use when current alone is being transported, they are not necessarily suitable for use when drug is being transported, either because the solvent used may react adversely with or hinder the drug's delivery to a body surface, or because the constituents incorporated therein may interfere with drug transport.
One attempt to solve this incompatibility was to incorporate drug into a self-adhering drug reservoir comprised of a gel formed from a hydrophilic natural or synthetic material such as a natural resinous polysaccharide, plasticized with water and/or polyols, U.S. Pat. No. 4,474,570, which is incorporated herein by reference. However, it is not always desirable to use a self-adhering drug reservoir and it is not always possible such as when there is a rate controlling membrane positioned between the drug reservoir and the skin.
This invention therefore provides an adhesive formulation which overcomes many of the disadvantages associated with state of the art adhesives and is particularly suited for use as an in-line contact adhesive in electrically assisted drug transport systems.